Unsteady Flamelet Modeling of NOx and CO Formation in Hydrocarbon Diffusion Flames PDF Download
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Author: Naif Mohammed Al-Abbadi
Publisher:
ISBN:
Category :
Languages : en
Pages : 426
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Book Description
Author: Naif Mohammed Al-Abbadi
Publisher:
ISBN:
Category :
Languages : en
Pages : 426
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The formation of NO and NO2 are sensitive indicators of both temperature and residence time. In this work, the NOx emission index is measured in an unsteady counterflow diffusion flame for methane, propane and ethylene, as a function of average strain rate and amplitude and frequency of imposed sinusoidal oscillation. The flames studied vary from non-sooting to high soot loading, and from low average strain rate to near extinction. Due to the relatively long time scales associated with NOx formation, the effect of unsteadiness on emission index is weaker than on either temperature or soot volume fraction. Time average global measurements were taken using a California Analytical Instruments Model 400 HCLD NO/NOx analyzer. Results are compared with unsteady calculations using a modified OPPDIF code included in the Chemkin package.
Author: Weizhen Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages : 576
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Book Description
Author: Christopher Dwayne DeBruhl
Publisher:
ISBN:
Category :
Languages : en
Pages : 67
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Book Description
Keywords: Counterflow diffusion flames Nox.
Author: Howard G. Maahs
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 62
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Author: N. Al-Abbadi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: N. K. Rizk
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
A study is made of the influence chemical structure of fuel has upon combustion performance through tracing the generation of carbon monoxide and oxides of nitrogen in lean, premixed, hydrocarbon-air flames. The study includes both analytical and experimental investi- gations. On the analytical side, a kinetic model is developed to predict both CO and NO time-histories in one-dimensional, premixed flames. The model is based upon the assumption of partial equilibrium in the post-flame zone while the fuel oxidation in the main reaction zone is allowed for by using a global oxidation rate equation. NO formation is assumed to be entirely via the Zeldovitch mechanism and to start in the post-flame zone. The utility of the model is judged through comparison between theoretical results and experimental data. On the experimental side, a simple burner system, supporting a one-dimensional premixed flame was designed and built. All fuels selected for investigation were pure hydrocarbons representing the main hydrocarbon types usually found in practical fuels; namely paraffins, olefins, naphthenes and aromatics. The hydrogen-to-carbon ratio ranged from 1 to 2.67 and the carbon number from 3 to 12. The experiments were performed at 1,2 and 3 atm pressure levels and 140°C inlet temperature, while the equivalence ratio was in the range 0.6 to 0.9. Flames were sampled for most stable species by a water- cooled stainless steel sampling probe. The experimental results show that the fuel structure signifi- cantly affects CO time-histories in the investigated flames mainly through influencing its generation rather than its burnout. CO burnout is shown to be mainly controlled by radical recombination processes, and the experimentally derived CO global oxidation rate equations are found not to be universally applicable. The results also show that the fuel structure influences prompt NOx formation within, and very near, the main reaction zone but that it does not influence post-equilibriu.
Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 712
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Author: Hongtao Yang
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :
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Book Description
Turbulent lean premixed combustion now plays a predominant role in reducing emission of pollutants such as NOx. For turbulent premixed flames located in the thin-reaction-zones regime, small-scale eddies could penetrate into the preheat zone of the flames and enhance the mixing process. In this study, the effects of small-scale turbulence on emission (NOx and CO) formation in premixed flame fronts are investigated through the incorporation of turbulence induced diffusion in the preheat zone of one-dimensional premixed flames. One-dimensional methane/air premixed flames are simulated with the 53-species GRI-Mech 3.0 mechanism at both atmospheric and engine conditions with different turbulence intensities. It is found that the NO generated in flame fronts deceases with increasing intensity of small-scale turbulence and the effect is more profound at high pressures. At high pressures, the turbulence induced diffusion in the preheat zone can reduce the NOx formation in flame fronts by more than 40%. On the other hand, the CO mass fraction in flame fronts increases with increasing intensity of small-scale turbulence. In the cases considered, the CO mass fraction in the flame fronts can increase by more than 55%. In addition, a flamelet-based approach that accounts for the flame thickening effects has been formulated to simulate NOx and CO formation in turbulent lean premixed combustion. In this approach, the species NO and CO are transported and solved in a simulation with chemical source terms being pre-calculated from 1-D premixed flames with detailed chemical kinetics and turbulence induced diffusion. The NO source term can be quantified by its formation in flame fronts and its formation rate in post-flame region. The CO source term can be calculated through its mass fraction at flame fronts, its mass fraction in the post-flame region and an oxidation time scale. The effect of heat loss on NO formation has been studied by investigate the relation between post-flame NO formation rate and flame temperature. Meanwhile, the effect of turbulent-chemistry interaction on NO were studied. The flamelet-based emission model has been implemented into Fluent and 3-Dimensional simulations were conducted in a combustion rig.
